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Determining baseband S/N ratio and link margin for a satellite link

  1. Jul 10, 2011 #1
    Hi everyone,
    I'm not sure if this is the right section to post this in, but the question doesn't really seem to fit any singular category, so I'll try this one (if someone has a better recommendation, please let me know!)

    The question I'm seeking to answer is this:

    A baseband signal of maximum frequency equal to 3.4 KHz is used in a SCPC-FM satellite link. A subjective improvement in baseband SNR of 7 dB is provided by de-emphasis. If the CNR of the receiver is 13 dB, calculate the baseband SNR ratio for the voice channel. If the FM demodulator has one FM threshold at 6 dB, estimate the link margin for this system. Take the RF channel bandwidth of the link as 45 KHz.

    What I really need is a boost to get started. I'm confused by a few things. First, the 'subjective improvement of 7 dB' is something I have no idea what that means.

    What I'm considering is using Carson's rule and then using the S/N formula for baseband FM.
    (I apologize, this is my first time in the formum, so I'm still learning how to type formulas)
    (S/N) = 3m^2*B/(2fm)*C/N*pw
    where m = peak frequency/highest frequency present in modulation signal
    B is what is determined from Carson's rule
    pw is a subjective improvement factor
    C/N is the carrier to noise ratio
    and fm is the highest frequency present in the modulation signal

    If I consider the 6 dB to be the carrier-to-noise ratio, I'd only need to determine the Carson's rule stuff and plug in. Am I right in thinking about it this way? Or am I way off base?

    And the only other problem is that I'm not sure exactly how to plug in what I'm given to the formula, because I'm not sure if I'm given a peak frequency, highest frequency in the modulation signal, etc.

    Can someone help to unconfuse me? Again, I'm not asking someone to do the problem for me, I just need a little help to get started.
    Last edited: Jul 10, 2011
  2. jcsd
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